The present invention relates to new compositions of polyarylalkane oligomers containing xylene units, a process for their manufacture, and products utilizing such compositions.
These products can be used as a microencapsulation solvent for rupturable microcapsules used to make carbonless transfer paper and for other products for which microcapsules can be used.
In Patent EP No. 136,230, the person skilled in the art has already proposed mixtures of oligomers based on benzyltoluene, dibenzyltoluene and ditolylphenylmethane, which exhibit the advantage, when compared with these same oligomers taken separately, of crystallizing at very low temperature and of having a viscosity which is always compatible with their application as a dielectric for capacitors.
These characteristics make them most particularly suitable for use as a microencapsulation solvent for microcapsules for such uses as in making carbonless transfer paper. However, they have a characteristic which disqualifies them for such use; namely, a highly unpleasant odor which is disclosed just like the color when the microcapsules are ruptured, at the time of hitting the keys of a typewriter, for example. The compositions according to the present invention not only have a viscosity which is compatible with the application, but are also characterized by an "absence of odor" which is absolutely essential in the intended application as a microencapsulation solvent for forming microcapsules.
Patent GB No. 1,346,364 summarizes the properties which must be reconciled in microencapsulation solvents:
(i) dissolving the color-forming material, such as a dye,
(ii) not evaporating when the microcapsules are processed,
(iii) being inert towards the encapsulation material,
(iv) not reacting with the solvent developer,
(v) having a viscosity which is low and relatively insensitive to temperature, and
(vi) not having an unpleasant odor.
Since the disadvantages of mono- and dibenzylalkylbenzenes have also long been known, many substitute mixtures have been proposed, starting with polyarylalkane oligomers. However, it is always difficult to reconcile the quality of the properties of the products obtained with the economic aspect of the means for producing this substitute product.
Thus, U.S. Pat. No. 3,939,095 describes methylphenyl(2,5-dimethylphenyl)methane or 2-xylylpara-xylene, the synthesis of which may be carried out by reaction of methylbenzyl chloride with para-xylene, followed by a separation to gain access to this oligomer in a pure form.
Lastly, in Japanese Patent Application JP-Kokai No. 73-86,612 reference is made to the use of, as a microencapsulation solvent of di(propylbenzyl)propylbenzene, the preparation of which calls for several stages with purifications at each stage and, consequently, in addition to the economic aspect, and just like the preceding patent, presents problems of effluent discharge and environmental problems.
As a general rule, the development of products which are particularly adapted for application as a microencapsulation solvent, for example, of the monoxylylxylene type, has met with success only through the use of relatively nonselective syntheses to obtain these products.